Universal fixture for holding printed circuit boards during processing

ABSTRACT

The present invention is a universal fixture for holding printed circuit boards with different sizes and shapes during, stencil printing and other manufacturing processes related to printed circuit boards. In one embodiment, a universal fixture for holding a printed circuit board has a platform with a work surface, a first support member attached to the platform to hold a portion of a printed circuit board, and a second moveable support member attached to the first support member to support another portion of the printed circuit board. The platform is preferably adapted to be attached to a workstation of a processing machine, such as a stenciling machine for printing solder or adhesive onto the printed circuit board. The first support member preferably has an elongated sidewall, a first endwall extending transversely from the sidewall, and a second endwall spaced apart from the first endwall along the sidewall and extending transversely from the sidewall. The sidewall and both the first and second endwalls preferably project away from the work surface of the platform to define a first support rim spaced apart from the work surface. Additionally, the second support member is preferably spaced apart from the sidewall and extends from the first endwall to the second endwall. The second support member preferably translates along the first and second endwalls to adjust the distance between the sidewall and the second support member such that the first and second support surfaces support perimeter regions of printed circuit boards with different sizes along the dimension between the second support member and the sidewall.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a divisional application of U.S. patent applicationSer. No. 08/761,701, filed Dec. 6, 1996, which has now issued as U.S.Pat. No. 5,779,794.

TECHNICAL FIELD

The present invention relates to processing printed circuit boards, andmore specifically to an apparatus that holds printed circuit boardsduring stencil printing processes for surface mounting components on theprinted circuit boards.

BACKGROUND OF THE INVENTION

Printed circuit boards ("PCBs") with electrical components are used incomputers, communications equipment, televisions, and many otherproducts. In typical applications, through-hole mounting and surfacemounting techniques are used to attach electrical components to the topand/or bottom surfaces of PCBs. Since the electronics manufacturingindustry is highly competitive, it is important to maximize thethroughput of PCB processing and to securely attach the electricalcomponents to the PCBs.

To surface mount components to a PCB, a solder and/or an adhesivecompound is deposited onto the surfaces of the PCB, and then thecomponents are pressed against the solder/adhesive. The solder/adhesiveis preferably deposited onto the PCB with a highly accurate stencilingmachine. Conventional stenciling machines generally have a stencilplate, a moveable work platform under the stencil plate, and a PCBholder attached to the platform. Conventional stenciling machines alsohave two spaced-apart, parallel conveyor tracks that transport the PCBalong a conveyor line below the stencil plate but above the moveableplatform.

In operation, the conveyor tracks transport the PCB until it is over thePCB holder, and then the work platform moves upwardly to engage the PCBholder with the bottom side of the PCB and lift the PCB to the stencilplate. Once the PCB is pressed against the stencil plate, a wiper movesacross the stencil plate to press a solder or an adhesive through holesin the stencil plate and onto the top surface of the PCB. The workplatform then moves downwardly away from the bottom surface of thestencil plate to replace the PCB on the conveyor rails.

Although conventional stenciling machines work well for processing largequantities of PCBs with a single size and shape, they are not wellsuited for contract PCB manufacturing in which five or more runs of PCBswith different sizes and shapes are processed in a single day. Oneproblem with conventional PCB stenciling machines is that conventionalPCB holders typically have a single size and shape to hold a single typeof PCB. As a result, to adapt conventional stenciling machines to printon PCBs with different sizes and shapes, custom PCB assembly lines aretypically shut down several times each day to replace one PCB holderwith another having a different size. It will be appreciated that thedowntime to change out the PCB holders significantly reduces thethroughput of a PCB assembly line. Therefore, it would be desirable todevelop an apparatus that reduces downtime in stenciling a solder or anadhesive in contract PCB manufacturing.

Another problem with conventional PCB stenciling machines is that thetop surface of the PCB should be very flat as it presses against thebottom side of the stenciling plate to ensure that an adequate quantityof solder or adhesive is deposited uniformly across the PCB. To hold thePCB flat during the stenciling process, the PCB is generally attached tothe PCB holder by a vacuum drawn against the bottom side of a PCB.Although holding the PCB to the PCB holder with a vacuum is desirable,only fixed-sized PCB holders are currently used with vacuum mountingsystems to ensure that an adequate vacuum is maintained against thebottom side of a PCB. Therefore, it would also be desirable to develop avacuum mounting apparatus that reduces downtime in stenciling a solderand an adhesive in contract PCB manufacturing.

SUMMARY OF THE INVENTION

The present invention is a universal fixture for holding printed circuitboards with different sizes and shapes during stenciling and othermanufacturing processes related to printed circuit boards. In oneembodiment, a universal fixture for holding a printed circuit board hasa platform with a work surface, a first support member attached to theplatform to hold a portion of a printed circuit board, and a secondmoveable support member attached to the first support member to supportanother portion of the printed circuit board. The platform is preferablyadapted to be attached to a workstation of a processing machine, such asa stenciling machine for printing a solder or an adhesive onto theprinted circuit board. The first support member preferably has anelongated sidewall, a first endwall extending transversely from thesidewall, and a second endwall spaced apart from the first endwall alongthe sidewall and extending transversely from the sidewall. The sidewalland both endwalls preferably project away from the work surface of theplatform to define a first support rim spaced apart from the worksurface. Additionally, the second support member is preferably spacedapart from the sidewall and attached to the first endwall and the secondendwall. The second support member is adapted to translate along thefirst and second endwalls to adjust the distance between the sidewalland the second support member such that the sidewall and the secondsupport member support printed circuit boards with different sizes.

In another embodiment, a universal fixture for holding a printed circuitboard has a platform with a work surface and a plurality of wallsprojecting upwardly from the platform. The plurality of walls define anadjustable support rim that may be sized and shaped to support thebottom side of a printed circuit board with different sizes and shapes.The platform is preferably adapted to be attached to a workstation of aprinted circuit board processing machine, and the plurality of panelspreferably includes first, second, third and fourth panels that eachhave an elongated top edge. The first panel is positioned on the workplatform, and the second and third panels are attached to the firstpanel and extend transversely with respect to the top edge of the firstpanel. The second and third panels are also spaced apart from oneanother along a common side of the first panel. The fourth panel isspaced apart from the common side of the first panel, and at least oneof the first and fourth panels moves with respect to the other to adjustthe distance between the first and fourth panels. In one embodiment, thefourth panel translates along the second and third panels to selectivelyposition the elongated edge of the fourth panel a desired distance fromthe elongated edge of the first panel. Thus, the first and fourth panelsare positioned with respect to each other to support different printedcircuit boards with different sizes along the dimension between thefirst and fourth panels.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a side elevational view of a printed circuit board stencilingmachine in accordance with one embodiment of the invention.

FIG. 2 is a partial isometric view of the printed circuit boardstenciling machine of FIG. 1.

FIG. 3A is a cross-sectional view of the printed circuit board holderused in the embodiment of FIGS. 1 and 2 taken along the line 3A--3A ofFIG. 2.

FIG. 3B is a cross-sectional view taken along the line 3B--3B of FIG.3A.

FIG. 4A is a top plan view of the embodiment of the printed circuitboard holder of FIGS. 1 and 2 shown in one configuration.

FIG. 4B is a top plan view of the printed circuit board holder of FIG.4A in a different configuration.

FIG. 5 is a schematic top plan view of another embodiment of a printedcircuit board holder in accordance with the invention.

FIG. 6 is a schematic top plan view of another embodiment of a printedcircuit board holder in accordance with the invention.

FIG. 7 is a schematic top plan view of another embodiment of a printedcircuit board holder in accordance with the invention.

FIG. 8 is a schematic top plan view of still another embodiment of aprinted circuit board holder in accordance with the invention.

FIG. 9 is a schematic top plan view of a further embodiment of a printedcircuit board holder in accordance with the invention.

DETAILED DESCRIPTION OF THE INVENTION

The present invention is a universal PCB holder that supports PCBs withdifferent sizes and shapes during processing of the PCBs. An importantaspect of an embodiment of the invention is that the universal PCBholder has at least one adjustable support member that may be quicklymoved between runs of differently sized PCBs to change the dimensions ofthe PCB holder. Thus, PCBs with different sizes and shapes may beassembled without shutting down the PCB assembly line for significantperiods of time. FIGS. 1-9, in which like reference numbers refer tolike part throughout the various figures, illustrate printed circuitboard stenciling machines and universal PCB holders in accordance withthe invention.

FIG. 1 is a side elevational view and FIG. 2 is a partial isometric viewof a stenciling machine 20 in accordance with the invention fordepositing a solder and/or an adhesive onto a PCB. In one embodiment,the stenciling machine 20 has a moveable platform 32, a universal PCBholder 40 on the platform 32, conveyor tracks 70(a) and 70(b) outside ofthe PCB holder 40, and a stenciling assembly 90 above the conveyortracks 70(a) and 70(b). The platform 32 is attached to a number ofactuators 36 that raise and lower the universal PCB holder 40 to lift aPCB workpiece 80 off of the conveyor tracks 70(a) and 70(b). In apreferred embodiment, the platform 32 has a vacuum port 34 to which avacuum pump (not shown) may be coupled to draw a vacuum within the PCBholder 40 against the PCB 80. The stenciling device 20 preferably has ahousing 22 or other support structure to which the actuators 36, theconveyor tracks 70(a) and 70(b), and the stenciling assembly 90 areattached. One suitable stenciling machine that has a moveable platform32, conveyor tracks 70(a) and 70(b), and a stenciling assembly 90 is theUltraprint stenciling machine manufactured by MPM Corporation.

The PCB holder 40 shown in FIGS. 1 and 2 is a preferred embodiment ofthe invention that is adjustable in two dimensions. As best shown inFIG. 2, the PCB holder 40 preferably has first and second elongatedsidewalls or panels 42 and 44 extending along a lengthwise dimension Lof the PCB holder 40. Additionally, the PCB holder 40 preferably hasfirst and second elongated endwalls or panels 46 and 48 extendingtransversely to the first and second sidewalls 42 and 44 along awidthwise dimension W. The sidewalls 42 and 44 are preferablyfixed-length support members, and the endwalls 46 and 48 are preferablyadjustable-length support members that slide along the sidewalls 42 and44. Thus, to change the size of the PCB holder 40 along the lengthwisedimension L, the endwalls 46 and 48 are translated along the sidewalls42 and 44 to adjust the distance between the endwalls 46 and 48.Similarly, to change the size of the PCB holder 40 in the widthwisedimension W, the lengths of the endwalls 46 and 48 are changed to adjustthe distance between the sidewalls 42 and 44.

Referring to FIGS. 1 and 2 together again, the first sidewall 42preferably has a plurality of spaced-apart channels 51 extending in thelengthwise dimension L along at least a portion of the interior surface43 of the first sidewall 42. The second sidewall 44 similarly has aplurality of spaced-apart channels 53 (best shown in FIG. 1) extendingin the lengthwise dimension L along at least a portion of the interiorsurface 45 of the second sidewall 44. A plurality of slider blocks 47and 49 are slideably attached to the sidewalls 42 and 44. The sliderblocks 47 each have keys 57 that mate with the channels 51 and 53, andthe slider blocks 49 each have keys 59 that also mate with the channels51 and 53. The keys 57 and 59, and the channels 51 and 53 are preferablyshaped to hold the slider blocks 47 and 49 to the first and secondsidewalls 42 and 44 in a manner that allows the slider blocks 47 and 49to translate along the first and second sidewalls 42 and 44 in thelengthwise dimension L. In this embodiment of the invention, each end ofthe first endwall 46 is attached to a slider block 47 and each end ofthe second endwall 48 is attached to a slider block 49. Accordingly, theendwalls 46 and 48 are slideably coupled to the sidewalls 42 and 44 viathe slider blocks 47 and 49, respectively.

In a preferred embodiment, the first and second endwalls 46 and 48 eachhave a plurality of slideably connected elongated sections or panelsthat translate with respect to one another to adjust the lengths of thefirst and second endwalls 46 and 48. For example, the first endwall 46preferably has a first section 46(a) slideably connected to a secondsection 46(b), and the second endwall 48 preferably has a first section48(a) slideably connected to a second section 48(b). The first endwallsections 46(a) and 48(a) preferably have a plurality of elongated rails56(a) and 58(a), respectively. Conversely, the second endwall sections46(b) and 48(b) preferably have a plurality of channels 56(b) and 58(b),respectively. The rails 56(a) slideably mate with the channels 56(b) sothat the first and second sections 46(a) and 46(b) of the first endwall46 translate with respect to each other to adjust the length of thefirst endwall 46. Similarly, the elongated rails 58(a) slideably matewith the channels 58(b) so that the first and second sections 48(a) and48(b) of the second endwall 48 translate with respect to each other toadjust the length of the second endwall 48. Additionally, the first andsecond sections 46(a) and 46(b) of the first endwall 46 are preferablyeach attached to one of the slider blocks 47, and the first and secondsections 48(a) and 48(b) of the second endwall 48 are each preferablyattached to one of the slider blocks 49.

The walls 42, 44, 46 and 48 are preferably placed on the platform 32 tobe freely translated with respect to one another to adjust the size ofthe PCB holder 40. The walls 42, 44, 46 and 48 also project upwardlyfrom the surface of the platform 32 to define elongated support surfaces60 for holding the PCB 80 (shown in FIG. 1). Additionally, a seal 61(a)is preferably positioned on the top surfaces 60 of the walls 42, 44, 46and 48 to efficiently maintain a vacuum against the backside of a PCB.

FIG. 3A is a cross-sectional view of a preferred embodiment of theslideable connections between the second endwall 48 and the sidewalls 42and 44. In a preferred embodiment, each channel 51 has retainingsurfaces 62 that extend divergently from an elongated opening 61 at theinterior surface 43 of the first sidewall 42 to an intermediate pointwithin the first sidewall 42. Similarly, each channel 53 has retainingsurfaces 64 that extend divergently from an elongated opening 63 at theinterior surface 45 of the second sidewall 44 to an intermediate depthwithin the second sidewall 44. The keys 59 on the slider blocks 49preferably have divergent rims 59(a) that mate with the retainingsurfaces 62 and 64. The keys 59 are preferably shaped to fill thechannels 51 and 53, and to hold the slider blocks 49 against theinterior surfaces 43 and 45 of the sidewalls 42 and 44, respectively.Thus, the slider blocks 47 and 49 can translate along the sidewalls 42and 44 to adjust the distance between the endwalls 46 and 48 along thelengthwise dimension L and they allow a vacuum to be drawn in the PCBholder 40.

FIG. 3B is a cross-sectional view of a preferred embodiment of theslideable connections between the first and second sections 48(a) and48(b) of the second endwall 48. The rails 58(a) of the first section48(a) preferably have a cross-sectional shape similar to the keys 59 ofthe slider block 49. Similarly, the channels 58(b) of the second section48(b) preferably have a cross-sectional shape similar to the channels 51and 53 of the sidewalls 42 and 44. Additionally, the rails 58(a)preferably mate with the channels 58(b) to prevent substantial leakingbetween the first and second sections 48(a) and 48(b) of the secondendwall 48. The first and second sections 48(a) and 48(b) of the secondendwall 48 accordingly translate with respect to one another to changethe length of the second endwall 48 along the widthwise dimension W andthey allow a vacuum to be drawn in the PCB holder 40.

The first section 46(a) of the first endwall 46 has rails 56(a) similarto rails 58(a) of the second endwall 48, and the second section 46(b) ofthe first endwall 46 preferably has channels 56(b) similar to channels58(b) of the second endwall 48. Accordingly, the first and secondsections 46(a) and 46(b) of the first endwall 46 also translate withrespect to one another to adjust the length of the first endwall 46along the widthwise dimension W and allow a vacuum to be drawn in thePCB holder 40.

FIGS. 4A and 4B are top plan views of the PCB holder 40 illustratingdifferent configurations of the sidewalls and endwalls. Referring toFIG. 4A, the first and second endwalls 46 and 48 are configured in anextended position in which the first and second sidewalls 42 and 44 arespaced apart by a maximum distance in the widthwise dimension W. Thefirst and second endwalls 46 and 48 are also separated from one anotherby nearly the full length of the sidewalls 42 and 44 along thelengthwise dimension L. Accordingly, FIG. 4A illustrates the PCB holder40 in a configuration to support a relatively large PCB.

FIG. 4B illustrates the first and second endwalls 46 and 48 in acontracted position to reduce the distance between the first and secondsidewalls 42 and 44 across the widthwise dimension W. The slide blocks47 and 49 are also moved along the first and second sidewalls 42 and 44to reduce the distance between the endwalls 46 and 48 along thelengthwise dimension L. The top surfaces 60 of the sidewalls 42 and 44,and the endwalls 46 and 48 are accordingly configured to support a PCBwith smaller dimensions along the widthwise dimension W and thelengthwise dimension L than the configuration of the PCB holder 40illustrated in FIG. 4A. It will be appreciated that FIGS. 4A and 4Billustrate only two configurations of the PCB holder 40, and that thewalls 42, 44, 46 and 48 may each be selectively moved to position thewalls under the desired portions of a specific PCB.

In an example of the operation of the stenciling machine 20 shown inFIG. 1, the conveyor tracks 70(a) and 70(b) initially position the PCB80 over the PCB holder 40. The actuators 36 then raise the platform 32until the PCB holder 40 lifts the PCB 80 from the conveyor tracks 70(a)and 70(b) and presses the PCB 80 against the bottom side of a stencilplate 92 of the stenciling assembly 90. A wiper assembly 96 of thestenciling assembly 90 then translates along a wiper track 99 to sweep awiper blade 97 across the top surface of the stencil plate 92 and drivea paste compound P through a pattern of holes 94 in the stencil plate92. After the paste P is printed onto the top surface of the PCBworkpiece 80, the actuators 36 lower the PCB holder 40 to replace thePCB workpiece 80 on the conveyor tracks 70(a) and 70(b). To stencilprint the paste compound P on another run of PCB workpieces having adifferent size than the PCB workpiece 80, the operator simply moves thestenciling assembly (90) out of the way and slides the walls 42, 44, 46or 48 of the PCB holder 40 to adjust the support surfaces 60 of the PCBholder 40 to hold the PCB workpieces having a different size. Forexample, the walls 42, 44, 46 and 48 may be adjusted as shown in FIGS.4A and 4B to hold workpieces having different sizes.

One advantage of a preferred embodiment of the universal PCB holder 40is that it may be quickly adjusted to support PCBs with different sizeswithout being removed from the stenciling machine. Unlike conventionalPCB stenciling devices in which the PCB holders have fixed sizes andmust be changed out to accommodate PCBs with different sizes, thespacing between the walls of the preferred embodiment of the PCB holder40 may be changed without removing the PCB holder 40 from the stencilingdevice 20. Therefore, the PCB holder 40 reduces downtime associated withchanging the stenciling machine 20 to accommodate runs of differentlysized PCBs in contract PCB manufacturing.

FIG. 5 is a top plan view that illustrates another embodiment of a PCBholder 140 that has tri-panel endwalls 146 and 148. More specifically,the first endwall 146 has a first end section 146(a) with a slider block47 attached to the first sidewall 42, a second end section 146(b) with aslider block 47 attached to the second sidewall 44, and an intermediatesection 146(c) slideably coupling the first end section 146(a) to thesecond end section 146(b) to allow the length of the first endwall 146to be adjusted along the widthwise dimension W. Similarly, the secondendwall 148 has a first end section 148(a) with a slider block 49attached to the first sidewall 42, a second end section 148(a) with aslider block 49 attached to the second sidewall 44, and an intermediatesection 148(c) slideably coupling the first end section 148(a) to thesecond end section 148(b). The endwalls 146 and 148 operate in much thesame manner as the endwalls 46 and 48 of the PCB holder 40 of FIGS. 1and 2. For example, the intermediate section 146(c) preferably has aplurality of rails 156 that slideably mate with channels 157 along theend sections 146(a) and 146(b), and the intermediate section 148(c)preferably has a plurality of rails 158 that slideably mate withchannels 159 along the end sections 148(a) and 148(b).

In another embodiment (not shown), the endwalls 146 and 148 may haveseveral intermediate sections slideably coupled together in the samemanner that the intermediate section 146(c) slideably couples the firstend section 146(a) to the second end section 146(b) of the first endwall146. In still another embodiment (not shown), one or both of theendwalls 146 and 148 may be fixedly attached to the sidewalls 42 and 44.

An advantage of the PCB holder 140 shown in FIG. 5 is that the minimumdistance between the sidewalls 42 and 44 across the dimension W is lesswith the endwalls 146 and 148 compared to the sidewalls 46 and 48 of thePCB holder 40 shown in FIGS. 1-4B. The sections of the endwalls 146 and148 extend across only slightly more than one-third of the maximum widthof the PCB holder 140, as opposed to the sections of the endwalls 46 and48 that extend across slightly more than one-half of the maximum widthof the PCB holder 40 (shown in FIG. 4A). Thus, when the endwalls 146 and148 are in the fully contracted configuration, the minimum distancebetween the sidewalls 42 and 44 is approximately one-third of themaximum width of the PCB holder 140.

FIG. 6 is a top plan view of another embodiment of a PCB holder 240 inaccordance with the invention. The PCB holder 240 has a first supportmember 241 with a sidewall 242, a first endwall 246 extendingtransversely to the sidewall 242, and a second endwall 248 spaced apartfrom the first endwall 246 along the sidewall 242 and extendingtransversely to the sidewall 242. The PCB holder 240 also has a moveablesecond support member 244 spaced apart from the sidewall 242. The secondsupport member 244 is preferably attached to slider blocks 245 that aresimilar to the slider blocks 47 discussed above with respect to FIG. 2.One of the slider blocks 245 is slideably received in a channel 256extending along the interior wall of the first endwall 246, and theother slider block 245 is slideably received in a channel 258 extendingalong the interior surface of the second endwall 248. The channels 256and 258 in the endwalls 246 and 248 of the first support member 241 arepreferably similar to the channels 51 and 53 in the sidewalls 42 and 44,as discussed above with respect to FIG. 2.

In operation, the second support member 244 translates along the firstand second endwalls 246 and 248 to position the sidewall 242 and thesecond support member 244 under perimeter regions of a specific PCB. ThePCB holder 240 is particularly advantageous to support PCBs that havethe same length along the lengthwise dimension L, but different widthsalong the widthwise dimension W.

FIG. 7 is a top plan view of another embodiment of a PCB holder 340 inaccordance with the invention. The PCB holder 340 has sidewalls 342 and344 that are slideably connected to endwalls 346 and 348. The sidewall342 has one slider block 343 slideably received within a channel 356 ofthe first endwall 346 and another slider block 343 slideably receivedwithin a channel 358 of the second endwall 348. Similarly, the sidewall344 has one slider block 345 slideably received within the channel 356of the first endwall 346 and another slider block 345 slideably receivedwithin the channel 358 of the second endwall 148. The combination of thefirst sidewall 342, and the endwalls 346 and 348, define a first supportmember 341 that is similar to the first support member 241 of the PCBholder 240 illustrated in FIG. 6. However, both the first sidewall 342and the second sidewall 344 translate along the endwalls 346 and 348 toadjust the distance between the endwalls 346 and 348. Accordingly, boththe sidewalls 342 and 344 of the PCB holder 340 may be positioned tosupport printed circuit boards with different sizes across the widthwisedimension W.

FIG. 8 is a top plan view of another embodiment of a PCB holder 440 inaccordance-with the invention. The PCB holder 440 has a first supportmember 441 with a sidewall 442, a moveable endwall 446 with a sliderblock 457 connected to the sidewall 242, and a fixed endwall 448extending transversely from the sidewall 442. The slider block 457slideably mates with a channel 451 along the sidewall 442 so that themoveable endwall 446 can translate along the sidewall 442 in thelengthwise direction L. The PCB holder 440 also has a second supportmember 444 with a first section 444(a) slideably connected to themoveable endwall 446, and a second section 444(b) slideably connected tothe fixed endwall 448. The first section 444(a) of the second supportmember 444 is also slideably connected to the second section 444(b) toadjust the length of the second support member 444 along the lengthwisedimension L. In a preferred embodiment, the first section 444(a) of thesecond support member 444 has a number of rails 445 slideably receivedin a number of channels 454 in the second section 444(b). Additionally,the first section 444(a) of the second support member 444 is preferablyconnected to one slider block 447 that slideably mates with a channel456 in the moveable endwall 446, and the second section 444(b) of thesecond support member 444 is preferably connected to another sliderblock 447 that slideably mates with a channel 458 in the fixed endwall448.

In operation, the second support member 444 translates along theendwalls 446 and 448 to adjust the distance between the sidewall 442 andthe second support member 444. The moveable endwall 446 also translatesalong the sidewall 442 and drives the first section 444(a) of the secondsupport member 444 along the second section 444(b) to adjust thedistance between the endwalls 446 and 448. Accordingly, the PCB holder440 is adjustable in two dimensions to accommodate PCBs with differentsizes along both the lengthwise dimension L and the widthwise dimensionW.

FIG. 9 is a schematic top plan view of still another embodiment of a PCBholder 540 in accordance with the invention. The PCB holder 540 has afirst support member 541 with a sidewall 542, a first moveable endwall546 with a slider block 557, and a second moveable endwall 548 with aslider block 559. The sidewall 542 preferably has a channel 551 in whichslider blocks 557 and 559 mate to allow the endwalls 546 and 548 totranslate along the sidewall 542. The PCB holder 540 also has a secondsupport member 544 slideably attached to the endwalls 546 and 548. Aswith the second support member 444 of the PCB holder 440, the secondsupport member 544 has first and second sections 544(a) and 544(b) thatslide with respect to one another. Also, the first section 544(a) of thesecond support member 544 has a slider block 547 slideably received in achannel 556 along the endwall 546, and the second section 544(b) has aslider block 549 slideably received in a channel 558 along the endwall548. In operation, the endwalls 546 and 548 translate along the sidewall542 to adjust the distance between the endwalls 546 and 548. Also, thesecond support member 544 translates along the endwalls 546 and 548 toadjust the distance between the second support member 544 and thesidewall 542.

The universal PCB holders illustrated in FIGS. 1-9 may be made from manymaterials, such as steel, aluminum, plastic, wood and polymericmaterials. In a preferred embodiment, the PCB holders are made from ahigh-density, low-friction material that is easily machined or processedto form the sidewalls and endwalls of the PCB holder. One suitablehigh-density, low-friction material for making a universal PCB holder inaccordance with the invention is Delrin® manufactured by E. I. du Pontde Nemours of Newark, Del.

From the foregoing it will be appreciated that, although specificembodiments of the invention have been described herein for purposes ofillustration, various modifications may be made without deviating fromthe spirit and scope of the invention. Also, even though the embodimentsof PCB holders in accordance with the invention have been described foruse in PCB stenciling machines, it will be appreciated that PCB holdersin accordance with the invention may be used in other PCB processingmachines (e.g., component mounting machines). Accordingly, the inventionis not limited to the embodiments and uses illustrated in FIGS. 1-9, butonly as by the appended claims.

What is claimed is:
 1. An adjustable fixture for supporting printedcircuit boards with different dimensions during processing, comprising:afirst panel having an elongated top edge, the first panel being adaptedto be positioned on a work platform of a printed circuit boardstenciling machine; a second panel abutting the first panel and havingan elongated top edge extending transversely with respect to the topedge of the first panel; a third panel abutting the first panel andhaving an elongated top edge extending transversely with respect to thetop edge of the first panel, the third panel being spaced apart from thesecond panel along a common side of the first panel; a fourth panelspaced apart from the common side of the first panel and attached to thesecond and third panels, at least one of the first and fourth panelsbeing moveable with respect to the other to adjust a distance betweenthe first and fourth panel to support printed circuit boards withdifferent dimensions, and wherein at least one of the second and thirdpanels is slideably attached to the first panel, and the fourth panelcomprises an elongated first section attached to the second panel and anelongated second section attached to the third panel, the second sectionbeing slideably connected to the first section to translate along alongitudinal axis of the fourth panel and adjust the length of thefourth panel as the at least one of the second and third panels slidesalong the first panel.
 2. The fixture of claim 1 wherein the elongatedfirst section of the fourth panel is slideably attached to the secondpanel and the elongated second section of the fourth panel is slideablyattached to the third panel.
 3. The fixture of claim 1 wherein thesecond and third panels are slideably attached to the first panel.
 4. Anadjustable fixture for supporting printed circuit boards with differentdimensions during processing, comprising:a first panel having anelongated top edge, the first panel being adapted to be positioned on awork platform of a printed circuit board stenciling machine; a secondpanel abutting the first panel and having an elongated top edgeextending transversely with respect to the top edge of the first panel;a third panel abutting the first panel and having an elongated top edgeextending transversely with respect to the top edge of the first panel,the third panel being spaced apart from the second panel along a commonside of the first panel; and a fourth panel spaced apart from the commonside of the first panel and attached to the second and third panels, atleast one of the first and fourth panels being moveable with respect tothe other to adjust a distance between the first and fourth panel tosupport printed circuit boards with different dimensions, and whereinthesecond panel extends between the first and fourth panels, and the secondpanel comprises an elongated first section attached to the first paneland an elongated second section attached to the fourth panel, the firstsection of the second panel being slideably connected to the secondsection of the second panel to provide translation between the first andsecond sections of the second panel for adjusting the length of thesecond panel, and the third panel extends between the first and fourthpanels, and the third panel comprises an elongated first sectionattached to the first panel and an elongated second section attached tothe fourth panel, the first section of the third panel being slideablyconnected to the second section of the third panel to providetranslation between the first and second sections of the third panel foradjusting the length of the third panel.
 5. The fixture of claim 4wherein the first section of the second panel is slideably connected tothe first panel and the second section of the second panel is slideablyconnected to the fourth panel, the second panel being translatable alongthe first and fourth panels to adjust a distance between the second andthird panels.
 6. The fixture of claim 5 wherein the first section of thethird panel is slideably connected to the first panel and the secondsection of the third panel is slideably connected to the fourth panel,the third panel being translatable along the first and fourth panels toadjust a distance between the second and third panels.